Hey! We are not the creators of multiplayer and we can't help you with that bug. If you message the creator of the multiplayer extension I'm sure that he will help you.
Thanks. We (the developers) do not use Mac ourselves and we do not know how to package it correctly. It would be great if you could tell us how to package a Mac version.
You definitely have good enough specs. Because you have a new graphics card try downloading the latest drivers for it and also make sure that you have Directx 11 installed.